Forget his age and his left handedness. When do guys with no plus pitches have long careers as elite pitchers? I know, everyone hates when I say the reason is he's deceptive because it's not quantifiable in the numbers sense, but he's the most deceptive pitcher in baseball and that's why he's succeeding more than anything else he brings to the table. Traditionally, that doesn't last. At least not at an elite level. There has to be something more.

When deciding an a pitcher- age and LH vs. RH are pretty big factors to consider.

I shared your concerns about Quintana in his first season- but he's now been around the league for 2 full seasons- and he's improving- not regressing- so I think you're over weighting the whole "deception" thing.